1. Field of Invention
This invention relates to a device for optimizing the operation of a nonlinear load, and particularly to a device for improving the power factor in an electrical power system and substantially eliminating harmonic currents generated by the nonlinear loads.
In electrical power systems, harmonic currents are often created due to the presence of nonlinear loads located therein. In some instances, significant levels of third order harmonic currents are created in electrical power systems having single phase nonlinear loads, which may often approach the level of the fundamental frequency current. Such third order harmonic currents adversely effect the performance of power systems by causing the peak voltage of the power lines to flatten, thus disrupting the operation of nonlinear loads, such as single-phase switching power supplies, and corresponding devices connected thereto.
Further, because harmonic currents in electrical power systems are additive in the neutral line, the harmonic currents in each phase line can greatly increase the amount of current in the neutral line, despite an even load distribution among the three phases in the power system. Such increases in the neutral current can result in voltage differences between the neutral and safety ground. In computer networks, for example, as these voltage levels approach the computer network signal levels, interference and data loss can result. Further, significant neutral current increases can cause the neutral lines and circuit breakers to be overloaded and overheated, which may possibly result in fires. Therefore, it is highly desirable to substantially eliminate harmonic currents in an electrical power system.
2. Description of Relevant Art
There are known inventions that improve the power factor of power systems or suppress harmonic currents generated therein. For example, U.S. Pat. No. 3,859,542 discloses compensation shunt circuitry for reducing harmonic currents when using nonlinear devices in power systems. However, by including capacitive reactive compensation in parallel to the devices, the invention includes an inherent overcorrection of the power factor.
Further, U.S. Pat. No. 4,961,044 discloses circuitry for improving the power factor of power supplies. This invention, though, fails to disclose a device adapted to be connected in series with a power supply, or a device for reducing neutral currents.
Additionally, U.S. Pat. No. 4,939,486 discloses a double-tuned shunt filter tuned to ordinal numbers 11 and 13 of the supply signal, and a high-pass filter in parallel therewith, both of which are adapted to reduce temperature variations thereof. This invention, however, fails to provide circuitry in series with a nonlinear load for reducing harmonic currents generated by the third harmonic, or for reducing neutral currents in an electrical power system.
Further, U.S. Pat. No. 4,812,669 discloses a device for suppressing harmonic currents using a passive filter tuned to high-order harmonic frequencies and an active filter tuned to low-order harmonic frequencies. However, the invention fails to provide a simply constructed, low power device for reducing neutral currents or third harmonic currents.